An electric vehicle or a hybrid electric vehicle (hereinafter, collectively referred to as ‘electric vehicle’) may be driven using electric energy of a battery in an electric drive mode. However, since such battery is a secondary battery and a function thereof is degraded as the battery repeats a charging/discharging, a degree of degradation thereof needs to be evaluated.
A state of health (SOH), which is a parameter quantitatively indicating characteristic change of capability of the battery due to an aging effect, is an index indicating how much the capacity of the battery has been degraded. The SOH is used to adjust charging/discharging capacity of the battery according to a replacement time point of the battery and a use time of the battery.
The characteristic change of the capacity of the battery may be estimated by internal resistance and temperature of the battery. Accordingly, according to the related art, after the capacity of the battery for each of the internal resistance and the temperature of the battery is measured in advance through a charging/discharging experiment, and a look-up table for mapping the SOH by relatively digitizing measurement capacity to initial capacity is obtained, the SOH corresponding to the internal resistance and the temperature of the battery was estimated.
In this case, since it is difficult to directly measure the internal resistance of the battery in a charging/discharging operation of the battery, a technology capable of accurately measuring the internal resistance of the battery is required.
In brief, the internal resistance of the battery may be indirectly calculated by applying Ohm's law to measured values of a voltage and a charging/discharging current of the battery. However, since the measured value of the voltage of the battery has a difference from an actual voltage due to an IR drop phenomenon of the battery, and the current of the battery also have a measurement difference, the SOH calculated by Ohm's law has large error.
As another method for estimating the SOH according to the related art for reducing the SOH error, there is a method for estimating a state of charge (SOC) of the battery by integrating the charging/discharging current of the battery, and estimating the SOH using the estimated SOC. However, the above-mentioned method had a problem that the measurement error occurring in an operation of measuring the current is accumulated and accuracy of the SOC used as basic data of the estimation of the SOH is decreased over time, which results in a degradation of reliability of the estimation of the SOH.